Rolling mill



Feb. 25, 1969 BAKER ETAL 3,429,166

ROLLING MILL Sheet Filed March 7, 1966 M/l ENTORS F F I w. A. BAKER ET AL 3,429,366

ROLLING MILL Filed March 7, 1966 Sheet 2 of 5 B FL .5.

lA/VE/VTORS iii/1.4mm 1o. GAKGL Jul/v #41211 6 06611?- GOULD A T TORNE Y Feb. 25, 1969 W. A. BAKER ETAL ROLLING MILL Filed March 7,

Sheet 3 of5 A TTORIVE 7 United States Patent 10,059/ 65 US. Cl. 72-242 Int. Cl. B21!) 13/14, 29/00, 31/32 9 Claims ABSTRACT OF THE DISCLOSURE A rolling mill, especially suited to prevent or correct bad shape of strip being rolled, has flexible work rolls each loaded by two or more rows of individually short backing rolls, which through carriers receive loading force so applied, as from hydraulic capsule means, as to be effective to provide substantially equal force from each backing roll on a work roll, the backing roll support also including resilient means, at least separately for the end backing rolls of each row, that can counteract the load force so as to permit compensation for mismatch between strip width and loaded length of work rolls.

The present invention relates to rolling apparatus for rectifying bad shape in rolled products or alternatively for producing rolled products in which bad shape is avoided or held to a minimum.

During rolling metal sheet is elongated and its thickness is reduced. If the elongation is not uniform across the width then the length of the sheet, when considered in an unstressed condition, will vary across the width. The short parts will be put in longitudinal tension and the long parts in longitudinal compression. If the length variations rise to such a level that the longitudinal stresses are large enough to cause buckling then the sheet will cease to lie flat and will be of bad shape.

Up to the point of buckling the relation between the length variations in the sheet and the corresponding stresses is proportional to the elastic modulus for the material in uniaxial tension or compression. The stress in any part is directly and linearly proportional to the length variation. Once the sheet has buckled it is no longer deforming in uniaxial compression and further increases in length variation are accompanied by increases in stress very much smaller than those which would occur in uniaxial compression.

If buckled sheet were forced to be flat then the short and long parts would be strained in uniaxial tension and compression respectively and the stresses, corresponding to the length variations, will be those proportional to the elastic modulus of the material. Thus the difference between the tensile and compressive stresses in a bad shape sheet are at a maximum when the sheet is held flat.

The critical stress or length discrepancy at which buckling occurs depends, for a given material, on the dimensions of the sheet.

In thick products the critical buckling stress is high and may correspond to a length discrepancy nearly equal to the maximum commercially tolerable degree of bad shape. In thin products the critical buckling stress is low and can correspond to length discrepancies much smaller than the maximum tolerable degree of bad shape. For example, considering the case of long edges, in plate /2 inch thick the critical buckling can correspond to a length discrepancy of 0.4% while the tolerable degree of bad shape corresponds to a length discrepancy of 0.41%.

3,429,1fifl Patented Feb. 25, 1969 On the other hand, in sheet 0.010 inch thick the critical buckling stress can correspond to a length discrepancy of 0.0003% while the tolerable degree of bad shape corresponds to a length discrepancy of 0.01%.

The basis of the present invention is the appreciation that if the pressure applied by the rolls is held constant across the width of the strip, then the degree of elongation will be dependent upon the secondary stresses acting longitudinally of the strip and that where the strip is under longitudinal tension it will elongate to a greater extent than where it is under longitudinal compression. with the result that the rolling of sheet material having bad shape under such conditions would result in a reduction of the length inequalities. Even greater reduction of length inequalities can be achieved if a greater pressure is applied by the rolls to the areas of strip under tension than to the areas under compression. In order to achieve the maximum correcting action the differences in the longitudinal stresses should be at their maximum values and this can best be achieved by ensuring that the strip or sheet is held flat both on the ingoing and outgoing side of the mill. This is most easily achieved by applying suflicient tension to the strip or sheet to hold it fast. The application of tension may only be necessary where the stresses due to localised differences in length are suflicient to cause buckling. In the case of thicker products, where the critical buckling stresses are not exceeded, the rolling of the product in the manner specified will have the eifect of reducing local inequalities of thickness and of reducing localised compressive and tensile stresses.

In order to achieve substantial equalisation of roll pressure at all positions across the width of the strip, the work rolls must be sufficiently flexible to match the cambers of normally rolled strip without giving rise to much variation of rolling load at different lateral positions, since this would result in bad shape.

A substantial degree of equalisation of rolling pressure can be achieved by backing the flexible work rolls by a series of short backing rolls arranged side by side, each of the backing rolls being pressed against the work roll by a substantially equal force. For practical success however it is necessary that the work roll should not be excessively flexible, since it is practically impossible to align the edges of the strip with the outer edges of the backing rolls adjacent the two edges with such exactness that the rolling load applied to the edges of the strip would not vary from the load applied in the middle of the strip by such an amount as to lead to bad shape, if the work roll was very flexible.

It is, in any event, desirable to be able to reduce the force applied by the backing rolls adjacent the edges of the strip.

The preferred means for equalisation of pressure on the backing rolls is a hydraulic capsule, mounted between the backing rolls and a rigid beam. The hydraulic capsule consists of a flattened envelope, filled with liquid, and adapted to work at internal pressure up to 500 psi.

In the accompanying drawings:

FIGURE 1 is a section of one form of mill constructed in accordance with the present invention,

FIGURE 2 is a plan view, showing the arrangement of the backing rolls,

FIGURE 3 is a section of an alternative form of mill, and

FIGURE 4 is a plan view of the arrangement of the backing rolls in the alternative construction of mill.

FIGURE 5 is an end view of a further alternative construction of mill.

FIGURE 6 is an end view of an alternative arrangement of work rolls and backing rolls.

FIGURE 7 is a diagrammatic end elevation of a drive for the work rolls.

In the construction shown in FIGURES 1 and 2 the work rolls 1 are of small diameter and are made quite flexible. The diameter of the work rolls 1 depends upon the service to be performed by the mill. Where the mill is to be employed for the rectification of aluminium container sheet, which has a thickness of about 0.0080.012 inch, a work roll of about 3 inches diameter is found to have flexibility characteristics which satisfy the criteria set out above. The work roll diameter would be increased to about 6 inches for aluminium sheet of a thickness of inch and up to about 9 inches for thicker sheet or plate. The considerations involved in selecting an appropriate roll diameter for the work rolls are discussed in greater detail below.

It is believed that any rolled sheet or strip will be acceptably fiat if the length discrepancies across its width do not exceed about 0.01%. On this basis acceptably flat low strength aluminium alloy sheet should be produced if the rolling load does not vary more than about 10% across the width of the sheet whereas for a strong aluminium alloy the corresponding acceptable loading error is believed to be about 2 /2 Each work roll 1 is backed by backing rolls 2, which are rotatably mounted in check plates 3, which are supported by a carrier beam 4. It will be seen in FIGURE 2 that the backing rolls 2 in the two rows are staggered in relation to each other. The backing rolls 2 may, alternatively, be arranged in opposed pairs in the two rows. The rolls 2 are preferably about 1-2 inches in length and the maximum spacing between longitudinally adjacent rolls is about /2 inch, preferably not more than about inch.

The carrier beam 4 is lightly constructed so as to be at least as flexible as the corresponding work roll 1. The flexible carrier beam 4 is supported within a rigid main beam 5 and is provided with guide rollers 6 to permit friction-free local movement of the carrier beam 4 within the rigid beam 5. A hydraulic capsule 7 is arranged between the carrier beam 4 and the rigid beam 5 and thus ensures that the carrier beam 4 is subjected to a substantially equal pressure throughout its length. The upper rigid beam 5 is supported by a screw 8 in a main frame 9 to permit variation of the gap between the work rolls 1.

The sheet 10, to be rectified to correct bad shape, is preferably progressed through the mill under tension. With the arrangement illustrated the tension on the ingoing and outgoing sides of the mill are equalised as far as possible and the work rolls are driven rolls.

The device used for drawing sheet through the mill under tension may comprise a movable gripper jaw of conventional construction. If a strip is being flattened in continuous length a pinch roll assembly, consisting of a driven steel roll and a idle rubber-covered roll, may be used as a tension source. This may be used alone or in conjunction with rubber-covered driven bridle rolls which would lower the tensions at the pinch to a level where slipping can be avoided with low pinch loads. Similar devices of conventional construction may be provided on the ingoing side of the mill to provide back tension.

In FIGURES 3 and 4, like parts are given the same references as in FIGURES 1 and 2. In this construction the backing rolls 2 are carried in pairs in individual carrier frames 12, which are pivoted by pivot pins 14 to the rigid main beam 5 on one side of the mill. As before the individual pairs of backing rolls 2 are subjected to an equalised loading from a hydraulic capsule 7, which presses against the backs of the carrier frames 12 to produce a moment about the pivots 14. Each carrier frame 12 is provided with a retaining hook 15, preferably loaded by means of a spring 16 and having an adjusting nut 17. The force due to the tensile or compressive stress in the issuing sheet acting on the rolls 1 at the roll bite has a moment about the pivots 14 and so a local increase in tensile stress will result in, by a local toggle action, a local increase in rolling load and hence an enhanced shape correcting local elongation. By incorporating this toggle action a more powerful means of correcting shape 4 errors in the strip is provided and also a means of reducing the errors which may be put into the strip by reason of the fact that the mill departs from the ideal design. Larger departures from the ideal design will be tolerable; for example the permissible degree of non-uniformity of loading will increase; the maximum roll diameter permitted will increase and the tolerable degree of mismatch between loaded width of the work rolls 1 and strip width will increase.

It is an observable fact however that when strip metal is being passed through a rolling mill under conditions which give rise to bad shape, and with the total tension greater on the outgoing side than that on the ingoing side, the tension in the strip on the ingoing side of the mill is subject to greater variation across the width of the strip than it is on the outgoing side of the mill.

Where the stress variations across the width of the strip are greater on the ingoing side of the mill than on the outgoing side of the mill the correcting effect will be improved by pivoting the carrier frames 12 on the ingoing side of the mill.

It is believed that this condition will obtain in all cases where the total tension on the strip on the outgoing side of the mill exceeds the total restraining tension on the strip on the ingoing side, as is the case when there is no drive on the work rolls.

On the other hand it is believed that the reverse condition can occur when the restraining tension on the ingoing side exceeds the tension on the outgoing side, as can be the case where the work rolls are driven.

In order, therefore, to permit the mill to perform under a variety of conditions, the carrier frames 12 will, in practice, in many cases be provided with means for pivoting them alternatively on the ingoing or outgoing sides of the mill.

This design of FIGURES 3 and 4 has two further advantages over that described in FIGURES 1 and 2. Uniform contact between all the backing rolls 2 and the work rolls 1 can be assured by making the pivot points adjustable. It is easy to ensure that the loaded width is no greater than the strip width by using the retaining hooks 15 and also it is easy by adjusting spring loading i on these retaining hooks, to provide loads to compensate for the mismatch between strip width and supported roll width. Thus the springs 16 may be compressed to lighten the loading on the backing rolls 2 at the edge of the sheet where the backing rolls are loading the work rolls over a width greater than the strip width.

In the construction illustrated in FIGURE 5 the same reference numerals are applied to like parts appearing in the FIGURES 1 to 4.

The construction of FIGURE 5 is designed to maintain alignment of the work rolls 1 in a simpler manner.

In this construction the ends of the main beams 5 are supported by a pair of upper and lower yoke members B and C. The yoke members B and C in each pair are connected to each other by a massive pivot A, which is carried in a bed plate (not shown). The main beams 5, and thus the operative spacing between the work rolls 1, are adjusted in relation to each other by means of threaded pillar members F supported in the bed plate. These pillar members may be rotated in any known manner and engage in threaded bosses D and E, carried by the yoke members B and C. The bosses D and E can, of course, swivel in relation to the yoke members in order to maintain their alignment with the related pillar member F. The ends of the work rolls 1 are free and are merely held in light locating plates, supported by the yokes B and C, so that the work rolls 1 cannot fall out when the yokes are opened. In this way a high degree of parallelism may be retained between the axes of the work rolls -1.

The pivots 14 in the constructions of FIGURES 3 and 4 and of FIGURE 5 are preferably approximately at the level of the contact of the back-up rolls 2 with the work rolls 1, so that the movement of the back-up rolls is substantially vertical, thus avoiding any substantial loading of the work rolls in the horizontal plane.

It will be understood that a Work roll 1 is located in lengthwise direction of the mill by its contact with two rows of backing rolls 2 or with the two intermediate rolls 21 and its co-operating work roll 1. In the direction transverse of the mill it may be found necessary to provide thrust bearings, which are floatingly guided in the frame, to prevent lengthwise movement of the work rolls.

It will be further understood that in constructions in which the work roll is in direct contact with the backing rolls it is possible to use more than two rolls of backing rolls, but the simplicity of using two rolls makes this the greatly preferred arrangement.

In the further modified construction shown in FIG- URE 6 the work rolls 1 are not in direct contact with the axially short backing rolls. In this case the work rolls 1 are in contact with a pair of thin, flexible intermediate rolls 21, which are located by their contact with the three backing rolls 22, carried as before in pivoted carriers 23, and with the work roll. The axial length of the backing rolls 22 is of the same order as that of the backing rolls 2 in the constructions of FIGURES l to 5, whilst the intermediate rolls 21 are substantially the same length as the work rolls 1. The pivoted carriers 23 are, as in the other constructions, subject to an equalised backing load which is transmitted to the work rolls 1 through the intermediate rolls 21.

The diameter of the intermediate rolls 21 is less than half, and preferably less than a quarter, of the diameter of the work rolls so that they do not add substantial extra stiffness to the system.

In the construction shown in FIGURE 6 there is no staggering of the work rolls in relation to one another. The purpose of the arrangement of FIGURE 6 is to further reduce the possibility of the formation of longitudinal marks on the rolled product. In the constructions of FIGURES 1 to 5, if the backing rolls are not staggered, there is a possibility of slightly greater wear of the work rolls 1 on those parts which are contacted by the backing rolls 2 than on those parts located between the backing rolls and such wear could lead to the formation of longitudinal lines on the final product. The construction of FIGURE 6 greatly reduces this possibility because there is no direct contact between the work rolls 1 and the backing rolls 22.

Whilst the invention has primarily been described in relation to its use as a means of rectifying rolled products, in which bad shape has been induced by existing rolling mills, a mill based on the Same principles may be utilised in both hotand cold-rolling to effect normal reductions of the order of 25% or more at each rolling pass and in such case the product should not require any final rectification treatment.

Where the mill is a driven mill, as is required if heavy reductions are to be taken, the work rolls 1 may be driven through an entirely conventional drive, such as that illustrated diagrammatically in FIGURE 7. In this figure the work rolls 1 are driven by shafts 30, through universal joints 31 and 32 from equal diameter pinions 33 in a pinion box 34, which receives drive through a reduction gear box 35 from a motor 36.

In addition to their ability to produce good shaped sheet products the mills above described also have the following advantages over conventional rolling mills.

(i) Gauge c0ntr0l.-The mill can give good uniformity of gauge along the length of the piece being rolled. The major elastic strains in the mill are those in the backing rolls and at the backing roll-work roll contact.

With small diameter work rolls and no conventional back-up rolls, roll eccentricity will be very small. Hence the mill will roll sheet with very much smaller short-term gauge variations in it than those which are unavoidable in sheet rolled on conventional mills.

(ii) Cooling and lubrication.l/Vith small diameter work rolls it is practical to use internal cooling so that the functions of roll cooling and roll bite lubrication can be separated from each other.

If, despite the use of internal cooling, thermal cambers are developed in the work rolls, then the work rolls can flex against the backing rolls to present a roll gap contour independent of the thermal cambers.

Mills made in accordance with this invention may be used as passive mills to effect light flattening drafts in conjunction with known front and back tension devices. Alternatively the work rolls may be driven to effect light flattening or larger rolling reductions, again in conjunction with known front and back tension devices. In many thin products the tensioning devices are essential to success ful use of these mills because they maximise the secondary stresses acting longitudinally in the material being rolled and exploit the shape correcting or shape preserving effects of these secondary stresses through the transverse softness and uniform loading of the new mills.

The maximum diameter of the work rolls to be employed in a rolling mill made in accordance with the present invention largely depends on the physical characteristics and gauge of the material to be rolled, whilst there is also a minimum diameter. necessary for torque requirements when the mill rolls are driven.

Whilst ideally the work rolls apply a uniform rollingpressure at all points across the width of the strip or sheet, this condition would require a completely flexible work roll. However if it is accepted that a rolled strip or sheet having length discrepancies of less than 0.01% will always be satisfactory, then the acceptable variations in rolling pressure across the width of the strip or sheet can be estimated by determination of the value of the following expression: 0.0001E/ Y, where E is Youngs modulus and Y is the yield stress of the strip.

In the case of aluminium alloys Y usually has a value in the range of 10,000-40,000 lbs./ sq. inch and E is approximately 10x10 lbs./ sq. inch. Thus the variation in rolling pressure should not exceed 2l0%, depending on the yield stress of the aluminium alloy concerned. Similar, but larger, variations in rolling pressures are permissible with mild steel.

In the case of thick aluminium strip and sheet it is not necessary to hold length discrepancies below 0.01% to avoid visible bad shape, but length discrepancies of say 0.05% are undesirable because of the high internal stresses in the product. The flexibility required in the work rolls of the present mill depends, in part, upon the accuracy to which the rolls can be ground truly cylindrical and straight. It is believed possible to grind rolls to a diameter accuracy of 0.0001 inch per 20 inch roll length; i.e. the roll diameter at one end will not be more than 0.0001 inch greater than the diameter at the other end of such 20" length and any change in diameter will be progressive. It is possible to estimate the maximum work roll diameter, assuming this degree of accuracy is achieved in grinding the working rolls, required for various rolling operations on aluminium alloys. These estimates are set forth in the following table and relate to work rolls made from the normal grades of steel used in mill rolls.

1 Torque for 60 wide strip and assuming a maximum stress of 4,000

pen.

2 Mill efiieiency assumed one-half for torque estimates.

In the mill described specifically above the loading applied to the work rolls is equalised along the length of the work rolls and it will be seen that providing the diameter of the work rolls is kept below the estimated maxima given above, the variations in pressure exerted by the work rolls across the width of the mill will be insufficient to cause the bad shape.

The use of flexible rolls, suitably vertically loaded, makes it possible to modulate the rolling load to correct bad issuing shape in the rolled product by sensing the stress discrepancies at different positions across the width of the outgoing strip and modulating the vertical loading at different positions across the strip width in accordance with the stress discrepancies thus detected. Thus each of the individual short back-up rolls may have a vertical load applied to them by hydraulic means in dependence upon the measurement of the stress in that part of the strip immediately adjacent to the back-up roll, instead of all the back-up rolls being subjected to an equal hydraulic backing loading.

Mills made in accordance with the present invention present a number of advantages as compared with conventional rolling mills. It is possible to employ true cylindrical work rolls in place of the cambered rolls employed in conventional rolling mills. It follows from this that it is unnecessary to change work rolls, as is necessary in conventional rolling mills when the width or thickness of the strip is changed and therefore, on balance, the extent of idle time is reduced.

The apparatus of the present invention can also be employed as a means for putting tension on strip or sheet. Because of the equalised loading applied by the work rolls across the width of the sheet it can be employed to apply tension without fear of inducing bad shape or buckling through localised differences in stretch.

We claim:

1. A rolling mill for strip material, comprising flexible upper and lower work rolls, a plurality of rows of rolls each having several axially short backing rolls for loading each of the work rolls, means for supporting said backing rolls for exertion of loading force between their surfaces and the surfaces of the work rolls loaded by said backing rolls, said supporting means including means for applying substantially equal loading force to each of the backing rolls in each row thereof, constructed and arranged to provide application of substantially equal force from the several rolls in each row to the work roll backed by said row, and resilient means associated wtih at least each of the backing rolls at each end of each row of backing rolls, separately for said end rolls from other rolls in the row, for counteracting the aforesaid loading force applicable from each backing roll with which such resilient means is associated, to permit compensation to be made for mismatch between the width of strip material passing through said rolling mill and the axial length of the work rolls that is loaded by said backing rolls.

2. A rolling mill as defined in claim 1, in which said supporting means for the backing rolls comprises individual carriers for said backing rolls, each carrying a backing roll in each of the rows for said exertion of loading force by the backing rolls, said mill having a rigid frame including rigid cross members, and said load-forceapplying means comprising hydraulic capsule means backed by a rigid cross member of said frame and hearing against the aforesaid individual carriers, for applying load force to the backing rolls.

3. A rolling mill as defined in claim 2, in which each carrier carries a plurality of backing rolls, being one in each of a plurality of rows,said plurality of rolls in each carrier being staggered in an axial direction in relation to each other.

4. A rolling mill as defined in claim 2, in which the individual backing roll carriers are pivoted to the rigid frame to permit vertical movement of the backing rolls.

5. A rolling mill as defined in claim 4, in which each carrier has a pivot axis, for such movement, which is disposed substantially at the level at which loading force is exerted on the work roll surface from the backing rolls.

6. A rolling mill as defined in claim 1, in which the supporting means disposes the backing rolls in direct contact with the work rolls.

7. A rolling mill as defined in claim 1, which includes intermediate flexible rolls disposed in contact with the work rolls and arranged between the work rolls and the load-supplying rows of backing rolls, said suppporting means disposing the backing rolls in direct contact with said intermediate rolls.

8. A rolling mill for strip material, comprising a rigid frame including rigid cross members, flexible upper and lower Work rolls, a plurality of rows of rolls each having several axially short backing rolls for loading each of the work rolls, and means including individual carriers for the backing rolls, for supporting said backing rolls for exertion of loading force between their surfaces and the surfaces of the work rolls loaded by said backing rolls, said supporting means including means for applying substantially equal loading force to each of the backing rolls in each row thereof, said load-force-applying means comprising hydraulic capsule means backed by a rigid cross member of said frame and bearing against the aforesaid individual carriers, for applying load force to the backing rolls of each row, to be effective substantially equally from each backing roll of the row upon the work roll loaded thereby.

9. A rolling mill for strip material, comprising flexible upper and lower work rolls, a plurality of rows of axially short backing rolls for loading each of the work rolls, the backing rollsin each row being axially spaced by distances substantially shorter than the axial length of each backing roll, means for supporting said backing rolls for exertion of loading force between their surfaces and the surfaces of the work rolls loaded by said backing rolls, said supporting means including individual carriers for the backing rolls in each row thereof, movable relative to the axes of the work rolls, and means for applying loading force substantially individually to the carriers for the backing rolls, said force-applying means being constructed and arranged to provide application of substantially equal loading force from the several rolls in each row to the work roll backed by said row, and a plurality of resilient means respectively individually associated with a plurality of backing rolls in each row thereof, including at least the backing rolls at each end of the row, for counteracting the aforesaid loading force applicable from each backing roll with which such resilient means is associated, said resilient means that have said force-counteracting effect for said end rolls being arranged to permit compensation to be made for mismatch between the width of strip material passing through said rolling mill and the axial length of the work rolls that is loaded by said backing rolls.

References Cited UNITED STATES PATENTS 1,824,211 9/1931 Jobke 72242 2,187,250 1/1940 Sendzimir 72242 2,651,954 9/1953 Dahlstrom 7 2243 2,828,654 4/ 1958 Ungerer 72242 2,907,235 10/ 1959 Murakami 72242 2,909,088 10/ 1959 Volkhausen 72243 3,049,949 8/ 1962 Volkhausen 72247 3,169,423 2/1965 Sims 72243 CHARLES W. LANHAM, Primary Examiner.

0 A. RUDERMAN, Assistant Examiner.

U.S. Cl. X.R. 

